So a paper onhow to build an atom bomb = legal.
A book on how to make a gun = illegal?
I don't know how many people remember, but President Clinton declassified and released nuclear weapons designs. Designs that we had never used (but that would work) were deemed overclassified due to a military culture of secrecy and declassified. They were then released under FOIA requests. I have no objection to digital files on firearms, but I had a huge problem with releasing "inefficient" nuke plans.
Yours is the best simplest explanation of this stupidity by leftist judges. I have 3D printed dolls for my granddaughters that have more brains than these leftist judges. I have downloaded plans for furniture, but it is easier to buy furniture. Same goes for making guns on 3D printers - it's at most a hobby thing but not practical as a threat thing.